EFFECT OF Ag ADDITION ON THE THERMAL STABILITY AND CATALYTIC PROPERTIES OF LaFeO3 PEROVSKITE

The effect of low Ag substitution in LaFeO3 perovskite on the thermal stability and catalytic oxidation of toluene was studied. Perovskites of the type La1-xAg xFeO3 (xAg =0.0, 0.05, 0.10) were prepared by the amorphous citrate method; characterized by nitrogen adsorption, XRD, FTIR, SEM-EDAX, TPR and O2- TPD techniques; and tested for the catalytic combustion of toluene in a flow reactor under excess oxygen. In comparison with the pure perovskite LaFeO3, the partially substituted La1-xAg xFeO3 present a perovskite structure with well-defined crystalline phases and greater reduction ability (attributable to the redox pair Fe+3/Fe+4). Noticeable changes in the á and ß-oxygen contents upon silver substitution were detected. Larger content of á-oxygen in the pure LaFeO3 perovskite is associated with greater catalytic activity. Two important effects upon Ag substitution in a pure LaFeO3 perovskites were observed: i) a greater reduction ability, ii) higher occurrence of oxygen vacancies due to ß-oxygen desorption, which were not active in the studied reaction.